Iv'e used PVC tubes many times, especially when I know I will be flying "grab your arse" airlines like the ones in Alaska. The pilot is usually the baggage handler, and none to happy bout it.

I have found that the PVC pipe (schedule 40 PVC) works better and is more durable then any tube sold for the purpose. Most tubes are thinner then schedule 40 pvc.

I was never that soffisticated and just capped one end with glue and the other with duct tape. But would be easy enough to drill hole thru cape and pipe and loop a long shaft padlock thru it.